Tetraglycidylamino compounds for producing useful as epoxy resins which exhibit low viscosity and good workability, and which give hardened products exhibiting excellent physical properties such as heat resistance, adhesion, rigidity, and mechanical strength. By virtue of these characteristic features, tetraglycidylamino compounds are used in a variety of fields and applications, including casting material, binder for carbon fiber composites, material used in the aerospace industry, material for electric and electronic parts, sporting goods, and polymer cross-linking agents.
Hitherto, there have been known methods for producing a tetraglycidylamino compound including a method in which a tetrahalohydrinamino compound having, on carbon atoms to each other, halogen and a hydroxyl group (hereinafter the compound may be referred to as a “halohydrin compound”) is formed through ring-opening addition reaction between an aromatic or alicyclic diamine and an epihalohydrin, and subsequently a tetraglycidylamino compound is produced through cyclization reaction (ring-closure reaction) of the halohydrin compound.
Japanese Patent Publication (kokoku) No. H08-32697 (Patent Document 1) discloses a method for producing a tetraglycidylamino compound, including forming a halohydrin compound through reaction between an aromatic or alicyclic diamine and an epihalohydrin, and subsequently performing cyclization reaction of the halohydrin compound twice by use of a dehalogenating agent (e.g., an alkali metal hydroxide) in the co-presence of a phase-transfer catalyst, wherein washing with water is carried out before and after re-cyclization reaction. This method is provided for producing a tetraglycidylamino compound which is generally used in electric and electronic fields, and which contains a hydrolyzable halogen in a minimum possible amount.
However, in the procedure of the Examples described in Patent Document 1, an epihalohydrin is recovered, through evaporation, from a reaction product produced through cyclization reaction of a formed halohydrin compound in the co-presence of a phase-transfer catalyst; the evaporation residue containing a tetraglycidylamino compound is dissolved in an organic solvent; washing with water is carried out a plurality of times; and cyclization reaction of the halohydrin compound is carried out again in an organic solvent in the co-presence of a phase-transfer catalyst, followed by washing with water a plurality of times. The specification of Patent Document 1 describes that washing with water before re-cyclization reaction is an essential step, and prevents coloring of a final product and improves the storage stability thereof, and that when washing with water is carried out two or more times before re-cyclization reaction, the washing effect is improved.
Thus, the tetraglycidylamino compound production method described in Patent Document 1 requires an increased number of steps, a long-term process, and very intricate operations (e.g., phase separation), since cyclization reaction is performed twice and repeated washing with water is performed. In addition, the production method poses problems in that a tetraglycidylamino compound is lost and the yield thereof is reduced, due to a large amount of wastewater and repeated phase separation operations; i.e., the method involves reduction in production efficiency and an increase in production cost.
Through the method described in Patent Document 1, there can be produced a tetraglycidylamino compound containing a reduced amount of a hydrolyzable halogen. However, this patent document does not disclose recycle of an organic solvent used in a water washing (i.e., washing with water) step and re-cyclization reaction.
In the method described in Patent Document 1, when an organic solvent is disposed of in every batch process without being recycled, the organic solvent is consumed in a large amount, and thus production cost increases, leading to an economical disadvantage. In contrast, when an organic solvent recovered through evaporation is recycled as is, an epihalohydrin used is gradually accumulated in the organic solvent, and thus the residual epihalohydrin and hydrolyzable halogen contents of a product of interest increase gradually, which is problematic.
In the method described in Patent Document 1, an alkali metal halide by-produced during cyclization reaction is dissolved in water and removed through phase separation, and subsequently washing is carried out with a large amount of water (i.e., 15 mol on the basis of 1 mol of a diamine serving as a raw material). In this case, an epihalohydrin and a tetraglycidylamino compound are discharged to some extent together with water, and the amount of loss of the tetraglycidylamino compound is not negligible.